The present invention relates to printing images on a print medium by depositing drops of a marking material, such as liquid ink.
Direct marking printers deposit a marking material, such as ink, onto a print medium, such as paper, to form images on the print medium. A common direct marking printer is the ink jet printer, which ejects drops of ink from an array of orifices on a printhead onto the print medium. The ink drops can be ejected from the printhead using thermal energy to form a gas or air bubble behind the ink drop in an orifice nozzle, or using electrical signals to alter the shape of piezoelectric material positioned to force a drop out of the orifice nozzle. Although the following description focuses on the use of piezoelectric drop ejection technology, those skilled in the art will recognize that the principles described are also applicable to other printing technologies, such as thermal ink jet.
A common construction of an ink jet printer includes a printhead that moves in a printing direction across the width of the print medium, depositing a set of ink drops on the print medium as the printhead moves to form an image swath on the print medium. After the printhead traverses the width of the print medium, the printer moves the print medium in a media travel direction, so that the printhead can again traverse the print medium and deposit another set of ink drops to form an additional image swath. Another construction of an ink jet printer includes a stationary printhead that extends across the full width of the print medium. The printhead deposits ink drops on the print medium as the print medium moves past the printhead.
Ink jet printheads are constructed to deposit ink drops at one predetermined density (dots per inch (dpi)) on the print medium in the printing direction, and also to deposit ink drops at another predetermined density (dots per inch) in a transverse direction, perpendicular to the printing direction. The dot density in the printing direction may be the same as, or different from the dot density in the transverse direction. Typically, the lower the ink drop density (the fewer dots per inch), the larger each dot is, to ensure full coverage of the print medium. The greater the dot density (more dots per inch), the smaller each dot is. Smaller, higher density dots tend to provide the edges of printed images with greater apparent sharpness. However, higher density printheads are more complex to manufacture, and controlling a larger number of ink ejectors to produce the greater number of ink drops requires a larger amount of data to be processed and transferred to the printhead.
An ink jet printer in accordance with the present invention includes a printhead and media movable with respect to one another in a printing direction. The printhead includes a plurality of ink outlets, each comprising two or more ink orifices, so that each ink outlet simultaneously ejects a set of at least two ink drops. The printhead additionally includes a plurality of ink ejectors for ejecting the ink drop sets from the ink outlets onto the print medium. Each ink ejector ejects one ink drop set from a multi-orifice ink outlet. The drops of each ink drop set are offset from one another in a transverse direction (perpendicular to the printing direction) by a transverse direction dot offset. A controller causes the printhead to deposit the ink drop sets with a printing direction dot set spacing (spacing between separate dot sets) that is approximately equal to the individual dot offset (between dots of a single dot set) in the transverse direction, reducing the number of control signals required to deposit dots. The printhead deposits small ink drops, so that the printhead can deposit the ink drops at a high frequency. The high frequency of ink drop deposit and small drop size permits high print resolution in the printing direction. The offset of the ink drops of each ink drop set in the transverse direction fills out the resulting printed image.
An example of a printhead for an ink jet printer in accordance with the present invention includes a printhead body having a printing direction and a transverse direction, and a plurality of ink delivery channels, and a plurality of ink outlets. Each ink outlet comprises a multi-orifice outlet from a corresponding particular one of the ink delivery channels, and each ink outlet comprises at least first and second ink orifices. The second ink orifice of each multi-orifice ink outlet is offset from the first ink orifice of that ink outlet in the transverse direction. The printhead additionally includes a plurality of ink ejectors. Each ink ejector simultaneously ejects from the first and second ink orifices of a corresponding particular ink outlet first and second ink drops.
A method of printing an image includes moving an ink jet printhead and a print medium relative to one another in a printing direction while using a single control signal to eject from a first multi-orifice ink outlet of the printhead a plurality of first ink drop sets and using a separate single control signal to eject from a second multi-orifice ink outlet a plurality of second ink drop sets. Ejecting from the first multi-orifice ink outlet each first ink drop set includes simultaneously ejecting a first set of ink drops that are offset from one another in a transverse direction, perpendicular to the printing direction, to form offset ink dot sets on the print medium, and ejecting from the second multi-orifice ink outlet each second ink drop set includes simultaneously ejecting a second set of ink drops that are offset from one another in the transverse direction to form offset ink dot sets on the print medium. The ink dot sets from the first multi-orifice ink outlet are spaced from one another by a printing direction dot set spacing. The ink dot sets from the second multi-orifice ink outlet are also spaced from one another by the printing direction dot set spacing. The ink dot sets from the first multi-orifice ink outlet are spaced from the ink dot sets from the second multi-orifice ink outlet in the transverse direction by a transverse dot set spacing that is greater than the printing direction dot set spacing.